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Separating ARP/ND cache maintenance from sending gratuitous ARP and UNAs #1342

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7eddca6
Separating ARP/ND cache maintenance, from sending gratuitous ARP and …
htibosch May 25, 2026
e2bec10
Some forgotten changes
htibosch May 25, 2026
d7f94e2
Cleaned up the changes, tested in real hardware
htibosch May 31, 2026
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88 changes: 46 additions & 42 deletions source/FreeRTOS_ARP.c
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Original file line number Diff line number Diff line change
Expand Up @@ -62,11 +62,6 @@
* entry is still valid and can therefore be refreshed. */
#define arpMAX_ARP_AGE_BEFORE_NEW_ARP_REQUEST ( 3U )

/** @brief The time between gratuitous ARPs. */
#ifndef arpGRATUITOUS_ARP_PERIOD
#define arpGRATUITOUS_ARP_PERIOD ( pdMS_TO_TICKS( 20000U ) )
#endif

/** @brief When there is another device which has the same IP address as the IP address
* of this device, a defensive ARP request should be sent out. However, according to
* RFC 5227 section 1.1, there must be a minimum interval of 10 seconds between
Expand Down Expand Up @@ -127,10 +122,6 @@

/*-----------------------------------------------------------*/

/** @brief The time at which the last gratuitous ARP was sent. Gratuitous ARPs are used
* to ensure ARP tables are up to date and to detect IP address conflicts. */
static TickType_t xLastGratuitousARPTime = 0U;

/**
* @brief Process the ARP packets.
*
Expand Down Expand Up @@ -226,8 +217,8 @@
FreeRTOS_OutputARPRequest_Multi( pxTargetEndPoint, pxTargetEndPoint->ipv4_settings.ulIPAddress );

/* Since an ARP Request for this IP was just sent, do not send a gratuitous
* ARP for arpGRATUITOUS_ARP_PERIOD. */
xLastGratuitousARPTime = xTaskGetTickCount();
* ARP for arpGRATUITOUS_ARP_PERIOD_MS, normally 300 seconds. */
vGARP_TimerReload( arpGRATUITOUS_ARP_PERIOD_MS );

/* Note the time at which this request was sent. */
vTaskSetTimeOutState( &xARPClashTimeOut );
Expand Down Expand Up @@ -943,6 +934,18 @@
eReturn = eARPGetCacheEntryGateWay( pulIPAddress, pxMACAddress, ppxEndPoint );
}

if( *ppxEndPoint != NULL )
{
struct xNetworkEndPoint * pxEndPoint = *ppxEndPoint;

if( ( pxEndPoint->bits.bEndPointUp == pdFALSE ) || ( pxEndPoint->pxNetworkInterface->bits.bInterfaceUp == pdFALSE ) )
{
/* _HT_ this printf is only used while testing. */
FreeRTOS_printf( ( "eARPGetCacheEntry: endpoint that serves %xip is not up.\n", ( unsigned ) ( *pulIPAddress ) ) );
eReturn = eResolutionFailed;
}
}

return eReturn;
}
/*-----------------------------------------------------------*/
Expand Down Expand Up @@ -1110,9 +1113,16 @@
* When the age reaches zero it is no longer considered valid. */
( xARPCache[ x ].ucAge )--;

if( xARPCache[ x ].ucAge == 0U )
{
/* The entry is no longer valid. Wipe it out. */
iptraceARP_TABLE_ENTRY_EXPIRED( xARPCache[ x ].ulIPAddress );
xARPCache[ x ].ulIPAddress = 0U;
}

/* If the entry is not yet valid, then it is waiting an ARP
* reply, and the ARP request should be retransmitted. */
if( xARPCache[ x ].ucValid == ( uint8_t ) pdFALSE )
else if( xARPCache[ x ].ucValid == ( uint8_t ) pdFALSE )
{
FreeRTOS_OutputARPRequest( xARPCache[ x ].ulIPAddress );
}
Expand All @@ -1127,21 +1137,21 @@
{
/* The age has just ticked down, with nothing to do. */
}

if( xARPCache[ x ].ucAge == 0U )
{
/* The entry is no longer valid. Wipe it out. */
iptraceARP_TABLE_ENTRY_EXPIRED( xARPCache[ x ].ulIPAddress );
xARPCache[ x ].ulIPAddress = 0U;
}
}
}
}
/*-----------------------------------------------------------*/

xTimeNow = xTaskGetTickCount();

if( ( xLastGratuitousARPTime == ( TickType_t ) 0 ) || ( ( xTimeNow - xLastGratuitousARPTime ) > ( TickType_t ) arpGRATUITOUS_ARP_PERIOD ) )
/**
* @brief Send a Gratuitous ARP packet to allow this node to announce the IP-MAC
* mapping to the entire network.
*/
void vARPSendGratuitous( void )
{
/* The IP-task is calling, allow it to actually send the packet. */
if( xIsCallingFromIPTask() )
{
NetworkEndPoint_t * pxEndPoint = pxNetworkEndPoints;
NetworkEndPoint_t * pxEndPoint = FreeRTOS_FirstEndPoint( NULL );

while( pxEndPoint != NULL )
{
Expand All @@ -1153,26 +1163,16 @@
}
}

pxEndPoint = pxEndPoint->pxNext;
pxEndPoint = FreeRTOS_NextEndPoint( NULL, pxEndPoint );
}

xLastGratuitousARPTime = xTimeNow;
}
}
/*-----------------------------------------------------------*/

/**
* @brief Send a Gratuitous ARP packet to allow this node to announce the IP-MAC
* mapping to the entire network.
*/
void vARPSendGratuitous( void )
{
/* Setting xLastGratuitousARPTime to 0 will force a gratuitous ARP the next
* time vARPAgeCache() is called. */
xLastGratuitousARPTime = ( TickType_t ) 0;
else
{
/* Let the IP-task call vARPAgeCache(). */
( void ) xSendEventToIPTask( eARPGratuitousEvent );
}

/* Let the IP-task call vARPAgeCache(). */
( void ) xSendEventToIPTask( eARPTimerEvent );
vGARP_TimerReload( arpGRATUITOUS_ARP_PERIOD_MS );
}

/*-----------------------------------------------------------*/
Expand All @@ -1189,7 +1189,11 @@
{
NetworkBufferDescriptor_t * pxNetworkBuffer;

if( ( pxEndPoint->bits.bIPv6 == pdFALSE_UNSIGNED ) &&
NetworkInterface_t * pxInterface = pxEndPoint->pxNetworkInterface;

/* If the interface is up, and it is an IPv4 end-point, and it has an IP address. */
if( ( pxInterface->bits.bInterfaceUp == pdTRUE ) &&
( pxEndPoint->bits.bIPv6 == pdFALSE_UNSIGNED ) &&
( pxEndPoint->ipv4_settings.ulIPAddress != 0U ) )
{
/* This is called from the context of the IP event task, so a block time
Expand Down Expand Up @@ -1300,7 +1304,7 @@

if( xLookupResult == eResolutionCacheMiss )
{
const TickType_t uxSleepTime = pdMS_TO_TICKS( 250U );
const TickType_t uxSleepTime = pdMS_TO_TICKS( 20U );

/* We might use ipconfigMAX_ARP_RETRANSMISSIONS here. */
vTaskSetTimeOutState( &xTimeOut );
Expand Down
18 changes: 18 additions & 0 deletions source/FreeRTOS_IP.c
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Original file line number Diff line number Diff line change
Expand Up @@ -323,13 +323,27 @@ static void prvProcessIPEventsAndTimers( void )
#endif /* ( ipconfigUSE_IPv4 != 0 ) */
break;

case eARPGratuitousEvent:
/* Send a Gratuitous ARP request. */
#if ipconfigIS_ENABLED( ipconfigUSE_IPv4 )
vARPSendGratuitous();
#endif /* ( ipconfigUSE_IPv4 != 0 ) */
break;

case eNDTimerEvent:
/* The ND Resolution timer has expired, process the cache. */
#if ipconfigIS_ENABLED( ipconfigUSE_IPv6 )
vNDAgeCache();
#endif /* ( ipconfigUSE_IPv6 != 0 ) */
break;

case eNDSendUNAEvent:
/* The ARP Resolution timer has expired, process the cache. */
#if ipconfigIS_ENABLED( ipconfigUSE_IPv6 )
vSendUnsolicitedNeighborAdvertisement();
#endif /* ( ipconfigUSE_IPv6 != 0 ) */
break;

case eSocketBindEvent:

/* FreeRTOS_bind (a user API) wants the IP-task to bind a socket
Expand Down Expand Up @@ -521,11 +535,15 @@ static void prvIPTask_Initialise( void )
#if ipconfigIS_ENABLED( ipconfigUSE_IPv4 )
/* Mark the ARP timer as inactive since we are not waiting on any resolution as of now. */
vIPSetARPResolutionTimerEnableState( pdFALSE );
/* Make sure the GARP timer is started. */
vGARP_TimerReload( arpGRATUITOUS_ARP_PERIOD_MS );
#endif

#if ipconfigIS_ENABLED( ipconfigUSE_IPv6 )
/* Mark the ND timer as inactive since we are not waiting on any resolution as of now. */
vIPSetNDResolutionTimerEnableState( pdFALSE );
/* Make sure the UNA timer is started. */
vND_UNA_TimerReload( ndGRATUITOUS_UNA_PERIOD_MS );
#endif

#if ( ( ipconfigDNS_USE_CALLBACKS != 0 ) && ( ipconfigUSE_DNS != 0 ) )
Expand Down
103 changes: 101 additions & 2 deletions source/FreeRTOS_IP_Timers.c
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Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,9 @@ static void prvIPTimerReload( IPTimer_t * pxTimer,

/** @brief ARP timer, to check its table entries. */
static IPTimer_t xARPTimer;

/** @brief Gratuitous timer, to send our IP-address unsolicited. */
static IPTimer_t xGratuitousTimer;
#endif
#if ipconfigIS_ENABLED( ipconfigUSE_IPv6 )

Expand All @@ -111,6 +114,9 @@ static void prvIPTimerReload( IPTimer_t * pxTimer,

/** @brief ND timer, to check its table entries. */
static IPTimer_t xNDTimer;

/** @brief Timer to send Unsolicited Neighbor Advertisements (UNA). */
static IPTimer_t xUnaTimer;
#endif
#if ( ipconfigUSE_TCP != 0 )
/** @brief TCP timer, to check for timeouts, resends. */
Expand Down Expand Up @@ -156,7 +162,15 @@ TickType_t xCalculateSleepTime( void )
uxMaximumSleepTime = xARPTimer.ulRemainingTime;
}
}
#endif

if( xGratuitousTimer.bActive != pdFALSE_UNSIGNED )
{
if( xGratuitousTimer.ulRemainingTime < uxMaximumSleepTime )
{
uxMaximumSleepTime = xGratuitousTimer.ulRemainingTime;
}
}
#endif /* if ipconfigIS_ENABLED( ipconfigUSE_IPv4 ) */

#if ipconfigIS_ENABLED( ipconfigUSE_IPv6 )
if( xNDTimer.bActive != pdFALSE_UNSIGNED )
Expand All @@ -166,7 +180,15 @@ TickType_t xCalculateSleepTime( void )
uxMaximumSleepTime = xNDTimer.ulRemainingTime;
}
}
#endif

if( xUnaTimer.bActive != pdFALSE_UNSIGNED )
{
if( xUnaTimer.ulRemainingTime < uxMaximumSleepTime )
{
uxMaximumSleepTime = xUnaTimer.ulRemainingTime;
}
}
#endif /* if ipconfigIS_ENABLED( ipconfigUSE_IPv6 ) */

#if ( ipconfigUSE_DHCP == 1 ) || ( ipconfigUSE_RA == 1 )
{
Expand Down Expand Up @@ -254,6 +276,13 @@ void vCheckNetworkTimers( void )
}
#endif /* if ipconfigIS_ENABLED( ipconfigUSE_IPv4 ) */

#if ipconfigIS_ENABLED( ipconfigUSE_IPv4 )
if( prvIPTimerCheck( &xGratuitousTimer ) != pdFALSE )
{
( void ) xSendEventToIPTask( eARPGratuitousEvent );
}
#endif /* if ipconfigIS_ENABLED( ipconfigUSE_IPv4 ) */

#if ipconfigIS_ENABLED( ipconfigUSE_IPv6 )
/* Is it time for ND processing? */
if( prvIPTimerCheck( &xNDTimer ) != pdFALSE )
Expand All @@ -279,6 +308,11 @@ void vCheckNetworkTimers( void )
iptraceDELAYED_ND_TIMER_EXPIRED();
}
}

if( prvIPTimerCheck( &xUnaTimer ) != pdFALSE )
{
( void ) xSendEventToIPTask( eNDSendUNAEvent );
}
#endif /* if ipconfigIS_ENABLED( ipconfigUSE_IPv6 ) */

#if ( ipconfigUSE_DHCP == 1 ) || ( ipconfigUSE_RA == 1 )
Expand Down Expand Up @@ -482,6 +516,71 @@ static void prvIPTimerReload( IPTimer_t * pxTimer,
#endif
/*-----------------------------------------------------------*/

#if ipconfigIS_ENABLED( ipconfigUSE_IPv4 )

/**
* @brief Sets the reload time of the ARP gratuitous timer and restarts it.
*
* @param[in] xTime Time to be reloaded into the ARP timer.
*/
void vGARP_TimerReload( const TickType_t uxTimeMs )
{
/* ulRandMs gives a random variation expressed in ms. */
/* E.g. every 300 seconds +/- 10% (randomized per endpoint). */
uint32_t ulRandMs = uxTimeMs;
TickType_t uxPeriod;
const TickType_t ulMaxMs = uxTimeMs / 10u;

xApplicationGetRandomNumber( &ulRandMs );

if( ulRandMs > ulMaxMs )
{
ulRandMs %= ulMaxMs;
}

uxPeriod = pdMS_TO_TICKS( uxTimeMs ) + pdMS_TO_TICKS( ulRandMs );
prvIPTimerReload( &xGratuitousTimer, uxPeriod );
FreeRTOS_printf( ( "vGARP_TimerReload: %u + %u = %u ms\n",
( unsigned ) uxTimeMs,
( unsigned ) ulRandMs,
( unsigned ) uxPeriod ) );
}
#endif /* if ipconfigIS_ENABLED( ipconfigUSE_IPv4 ) */
/*-----------------------------------------------------------*/

#if ipconfigIS_ENABLED( ipconfigUSE_IPv6 )

/**
* @brief Sets the reload time of a UNA:
* Unsolicited Neighbor Advertisements.
*
* @param[in] uxTimeMs Time (ms) to be reloaded into the timer.
*/
void vND_UNA_TimerReload( const TickType_t uxTimeMs )
{
/* ulRandMs gives a random variation expressed in ms. */
/* E.g. every 300 seconds +/- 10% (randomized per endpoint). */
uint32_t ulRandMs = uxTimeMs;
TickType_t uxPeriod;
const TickType_t ulMaxMs = uxTimeMs / 10u;

xApplicationGetRandomNumber( &ulRandMs );

if( ulRandMs > ulMaxMs )
{
ulRandMs %= ulMaxMs;
}

uxPeriod = pdMS_TO_TICKS( uxTimeMs ) + pdMS_TO_TICKS( ulRandMs );
prvIPTimerReload( &xUnaTimer, uxPeriod );
FreeRTOS_printf( ( "vSUNA_TimerReload: %u + %u = %u ms\n",
( unsigned ) uxTimeMs,
( unsigned ) ulRandMs,
( unsigned ) uxPeriod ) );
}
#endif /* if ipconfigIS_ENABLED( ipconfigUSE_IPv6 ) */
/*-----------------------------------------------------------*/

#if ipconfigIS_ENABLED( ipconfigUSE_IPv6 )

/**
Expand Down
10 changes: 3 additions & 7 deletions source/FreeRTOS_IP_Utils.c
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Original file line number Diff line number Diff line change
Expand Up @@ -822,13 +822,9 @@ void prvProcessNetworkDownEvent( struct xNetworkInterface * pxInterface )

configASSERT( pxInterface != NULL );
configASSERT( pxInterface->pfInitialise != NULL );
/* Stop the Address Resolution timer while there is no network. */
#if ipconfigIS_ENABLED( ipconfigUSE_IPv4 )
vIPSetARPTimerEnableState( pdFALSE );
#endif
#if ipconfigIS_ENABLED( ipconfigUSE_IPv6 )
vIPSetNDTimerEnableState( pdFALSE );
#endif

/* Let the ARP and ND-timers vIPSetARPTimerEnableState()
* and vIPSetNDTimerEnableState() running. */

/* The first network down event is generated by the IP stack itself to
* initialise the network hardware, so do not call the network down event
Expand Down
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